The InSight mission logbook
In his logbook, Instrument Lead Tilman Spohn who is at NASA in Pasadena, USA, gives us the latest updates regarding the InSight mission and our HP3 instrument - the 'Mole' - which will hammer into the Martian surface.##markend##
Logbook entry: 6 May 2019
It is been about a month since my last newsletter and it is about time to report on how things have evolved. The interpretation of the seismic data have settled to a value of 70-80 msec as already reported for the time interval between the first hammer stroke and the first substroke. This value is inbetween the extremes for a freely bouncing mole (50msec) and a mole progressing normally (100msec). The interpretation is that the mole has some hull friction but not enough to make substantial progress. Temperature measurements using the TEM-A sensor package on the mole indicate that the thermal resistance has decreased suggesting improved contact between the mole and the regolith. How that could have happened is not entirely clear but it could be that the regolith has relaxed to some extent improving thermal contact and friction.
Our camera expert have been able to devise a pose of the arm and the camera and suitable lighting conditions to clearly image the tether through a window in the “chimney” of the support structure (see below). The "chimney" is where the mole was housed before it started penetrating; the tether pulled by the mole is running through that chimney.
It is interesting to see that the tether bends over at the top. This observation has been used to confirm the mole length in the ground of 30cm by comparing the image with emulations with the flight spare model in the labortory. Comparison with earlier but less well lighted images even suggest that the mole has moved slightly during the diagnostic hammering! Thus, it is suggested that observing the tether through the window is likely the most direct observation of any mole downward movement. The team has thus decided to do another two rounds of diagnostic hammering in the late afternoon when the lighting conditions are most favorable and take a movie of the support structure and the window. Two rounds for safety reasons instead of one longer hammering round. Dividing the hammering that way allows a check during what space engineers call a “ground-in-the-loop” to see that nothing unexpected has happened. Unfortunately, there have been delays, first because of a temperature issue and an second an issue with the arm, both related to cautious safety regulations. But we should be able to do the first round of what we call diagnostic hammering #3 (#2 was commanded but not executed because of the issues) tomorrow. It will be interesting to see whether we see movements of the tether.
In parallel with the preparations for diagnostic hammering we are doing testing in the lab (where the mole proves to be robustly able to penetrate nicely through various sands and gravel push aside stones etc at least under Earth gravity) and tests at JPL and model calculations at DLR emulating possible operations with the arm and the support structure on Mars to either collapse the duricrust or increase the vertical stress and friction on the mole hull. Depending on the outcome of the diagnostic hammering, our next operation could be using the arm to load the support structure close to the fore-right-foot (the one you see in the image above) or the ground right next to the support structure near the tether box. These are spots believed to be close to the mole.
Otherwise, HP3 is entirely healthy
Logbook entry: 11 April 2019
It is about time to report on the progress that has been made since the last entry on March 22. After the diagnostic hammering was approved, it was actually commanded on the 25th, executed on Mars on the 26th and the first results were down on the 27th of March. However, the seismic data came only down by the end of that week and we had the first meeting to learn about the results on April 1st. Operations in Space take their time! As I have already described in earlier mails, the progress depends on commanding opportunities on Earth (3 per week), flybys of communication orbiters on Mars, and data downlink pipelines. Our discussions – now that the European teams are all back in home - use web communication interfaces and occur several times per week - early in the day in California, late in the afternoon in central Europe.
The diagnostic hammering was successful. The movie showed the Support Structure pitching forward as the mole hammered. The forward pitching could have been the result of the mole somehow pulling at the support structure or the shaking of the latter by the mole allowed it to "fall down" by about half or so of a centimeter. The seismic data are still under evaluation but if you recall that we were wondering whether the time difference between the two major hammer strokes was 50 or 100 msec, the results indicate that the measured value is somewhere in-between the two. No final value yet, but we may end up somewhere around 70-80 msec. What that means in terms of the mole movement must be assessed by the mole engineers!
The discussion about the reasons of the mole not penetrating further have settled to three hypotheses of similar credibility but differing likelihood of occurring:
1. The mole or the tether that it is trailing behind may be snagged in the Support Structure. While this hypothesis is credible it so far lacks a clear mechanism of how this may have happened. Tests at the DLR Institute of Space Systems have shown, that the tether may get snagged but only in very special circumstances. Still, a functioning model of the hardware has been shipped to JPL this weekend for engineers there to also check this possibility (BTW: It takes 2 entire weeks to clear customs over here for such a shipment. Add to that some time for customs clearing in the US)
2. The mole may have encountered a sufficiently large rock or stone at 30cm depth. The size of the rock would have to be 10cm or larger for the mole not being likely to push it aside or to go around it. This explanation is so simple that everybody would be ready to believe it. But, the likelihood of such a stone blocking the moles’ way is only a few percent judging from the well-established (surface) rock-size-frequency distribution for the landing site.
3. The mole may not have enough friction on the hull to balance the recoil (as explained in part in my earlier posts (e.g., the one of March 21st)). Consider hammering a nail into a wall. You need the wall to provide enough friction to the nail so that it will move forward and not simply rebound as you hit it with the hammer. In a similar way this is true for the mole. Although its internal masses and springs are dimensioned such that most of the energy is directed forward, there is a resulting force of about 7N that still needs to be balanced by hull friction from the sand around it. This would not be a severe problem if the sand were like quartz sand, for example, having no or little cohesion. What is a daily life analog? Well, consider sugar vs. flour. If you stick a finger in sugar and pull it back, the hole will disappear as the sugar will flow back into the hole you made. Try the same with flour! In this case, the hole will stay open. Sugar is cohesionless, while flour has cohesion. Geologists have seen in other missions on Mars that the Mars sand is cohesionless and therefore a borehole should collapse and provide pressure and friction to the mole hull. But geologists have also seen that the topmost centimeters on Mars is formed by what is called a "duricrust". Here, chemical reactions between grains of sand have made them stick together, providing cohesion in that layer. The duricrust is usually thin and not a problem. But at the InSight landing site, it seems to be 20 or so centimeters thick! If the mole is sitting in the duricrust, its hull may very well have lost friction and upon time, the mole may have widened the hole in the duricust as is suggested by the data from our accelerometer and by our thermal data. One may argue that the duricrust would likely collapse as the mole hammers through. Yes, but a hole a few times the moles diameter filled with collapsed duricrust is still likely to not provide enough pressure and thus friction to the hull. It should be said here that the Martian environment adds to the problem. Because the gravity is only about a third of the Earth’s the moles weight is of less help then it is on Earth. And the low atmosphere pressure of only 0.6% of the Earth’s amplifies the problem.
At the moment it seems that the discussion is leaning towards hypothesis #3, not the least as we have seen such a behavior in tests on Earth in cohesive sand and low atmosphere pressure. But we have not settled yet on this explanation. In any case, if hypothesis #3 were found to be the best explanation, it may also offer the simplest remedy. All we would need to do is help the mole to balance the recoil. The arm may be of help here but that needs to be assessed further by our engineers.
Otherwise, the mole is entirely healthy
Logbook entry: 22 March 2019
The Anomaly Response Team today has approved of our way forward. Accordingly, the next steps for HP3 will be:
Command a TEM-A thermal conductivity measurement today to be executed over the weekend. The measurement takes 24 hours. On Monday, command the diagnostic hammering and image taking I was describing in my previous post to be executed in the afternoon of the next sol on Mars with data being downlinked coming Wednesday. We may then have to take some time to evaluate the data.
Stay tuned and keep your fingers crossed!
Logbook entry: 21 March 2019
The InSight team is attending the Lunar and Planetary Science Conference in Houston, Texas, this week and at the time of this writing is presenting the first results of the mission to the interested scientific community. Bruce Banerdt, the mission PI, argued that the pace of this mission is slow because we are relying on stochastic processes and their results. While the lack of observation hitherto of a Mars-quake was still consistent with estimates of the Martian seismic activity, it was already clear that Mars cannot be as active as the Earth, which was, however, expected.
The stochastic results (the distribution of rock in the regolith) of a stochastic process (impacts) is still puzzling those who worry about the mole. This week we will have our third Anomaly Review Team meeting and we are seeking approval for a short diagnostic hammering cycle of 10-15 minutes length. Remember, the total numbers of strokes is a consumable (although we do not know for sure how many in total we will have, not until we have spent them all!). We want to use a particular filter on the short-period seismometer that will allow us a much better determination of the arrival times of the signals generated by the major hammer stroke and its strongest substroke. To understand that, we will have to dig a bit into the workings of the mole. Consider the image of the interior of the mole:
The motor (blue) pulls the hammer back (purple) and compresses the force spring until a mechanism releases the hammer which is then accelerated by the relaxing spring towards the inside of the tip. This provides the first and major hammer stroke. As a reaction of the hammer moving forward, the motor is moving backward and is compressing the back spring. When the back spring relaxes after being compressed to the maximum, it will accelerate the motor forward which eventually hits a latch in the casing and provides a second, smaller stroke, the first sub-stroke. Meanwhile, the hammer being repelled from the tip compresses the force spring again which on relaxing causes a third even smaller stroke.
We have shown that the short period seismometer can record at least the first sub-stroke in addition to the major stroke. We have further shown that the time between the sub-strokes is indicative of the motion of the mole. For example, if it is slowly moving forward, then the time difference will be about 100 milli-seconds. If it is rebounding while hammering against an obstacle, that difference will only be 50 milli-seconds. With a special filter applied to the short period data directly onboard the SEIS instrument, we will get a much better time resolution of the signals and should be able to diagnose whether or not the mole is stuck or even slowly moving forward or is rebounding. Knowing this will help us greatly in designing our strategy.
In addition, to the short period seismometer, the broad-band seismometer will be listening in, but with a filter specifically designed to prevent its ultrasensitive sensors from saturation. It is hoped that we will be able to derive a seismic velocity layering of the underground and see whether there is indication of a mechanically hard layer around 30 cm depth.
As a third diagnostic tool we will be using the IDC camera on the arm to take a movie of the support structure while the mole is hammering. Because the camera can only image about every fourth stroke, this is a bit experimental but the hope is that we can see the support structure either moving or not at all. An alternative considered to taking a movie would be to take a long-exposure image of the support structure while hammering.
If the project approves of the plan after a careful review, we should be able to command the experiment next week. However, it will take a while until the seismic data is fully downloaded and can be interpreted.
In the meantime laboratory and test bed experiments have started at DLR in Bremen and Berlin and at JPL in Pasadena. These aim at understanding the situation and how the mole got into it and how we may solve the problem. JPL has a functional model of the robotic arm that can be used and DLR will ship one of its fully functional hardware models to JPL.
Logbook entry: 12 March 2019
This week the radiometer has observed three passes of Phobos in front of the Sun: Phobos eclipses. The eclipses were pronounced in the radiometer data showing an approximately 1°C dip in temperature through the roughly 30 seconds of duration of the eclipse. The cameras on InSight have also observed the small and brief dip in daylight as can be seen in the animated gif below. The radiometer data will be interpreted in terms of the thermo-physical properties of the top-most layers of the Martian soil. Interpretations of the results are expected by the time of the Lunar and Planetary Science Conference earliest, which is from 18 to 22 of March.
Maybe you followed the Mars weather service at https://mars.nasa.gov/insight/weather/ as well as the virtual control room at https://www.musc.dlr.de/hp3/ and maybe you were wondering why the reported day-time temperatures are significantly different. While the weather service has a day-time maximum temperature of -13 to -15°C, on the MUSC server day-time temperatures go up to +15°C. The reason is that, while the weather service shows the air temperature, the MUSC server shows the so-called brightness temperature of the surface recorded as measured by the HP3 radiometer. The latter temperature is the temperature at which the Martian surface radiates heat while the air temperature is measured on a mast on the lander, a good metre above the surface. In more practical terms, the surface gets typically a good 20 to 30° degrees warmer than the air above the surface.
As for the Mole, it’s been a busy week with meetings and lots of brainstorming. The seismometer has recorded the hammering strokes which should be a useful tool for diagnosis (In addition, the data are of great scientific interest to the seismologists - and eventually geologists). For instance, a hammering stroke is actually two strokes (a major and a minor sub-stroke) that are about 1/10 of a second apart. The time difference between these strokes depends on the rate at which the Mole penetrates to depth. It is -in principle- the shorter, the faster the Mole moves forward. But if the Mole is not penetrating, but rather bouncing on the spot, the difference can be reduced from the value for normal slow penetration, too. Indications are that the two sub-strokes have been recorded by the short-period seismometer and are investigated. A thermal conductivity measurement has also been made and the data are awaiting downloading and interpretation.
This week, we will have a meeting of a larger team at JPL here to see where we are headed based on the evidence collected so far. The two most prominent hypotheses are 1) the Mole has encountered an obstacle (rock) and is hammering on the spot. In that case, it would be likely that it has widened the borehole it had been digging. An alternative is that 2) the Mole hardware got somehow snagged in the support structure because the Mole has been forced to egress at an angle of about 15°, most likely due to a shallow stone which it could, however, pass. As we have indirect evidence (that has been consolidating) that the mole is about ¾ of its length out and in the ground, it may be that it’s back part got snagged in the housing.
Logbook entry: 6 March 2019
Excellent news! We just got the data from the first Phobos eclipse observation and the cooling by the shadow passing through the fields of view of the radiometer in about 30 seconds is clearly visible. The cooling is by about 1°C and is thus somewhat larger than expected and certainly better than with the most pessimistic estimates (that would have said, we will not be able to see it at all)! So the team is happy and is rejoicing about the first eclipse on Mars ever observed with a radiometer.
What is the significance of the observation? There is a quantity that scientists call the thermal inertia. This quantity depends on the thermal conductivity of the near surface material, its density and its heat capacity. A small value indicates low thermal conductivity, for instance, or a large porosity (meaning low density) etc. The larger the thermal inertia, the smaller the effect. In particular, if the shadow moves through rapidly and the inertia is large, little effect will be measured. The measurable effect is the more pronounced the smaller the inertia. The team will now have to analyze the data and come up with a model of the uppermost millimeters or so of the surface material. So, it is part of our efforts to measure the geophysical paramters of Mars.
As for the mole, the team has commanded a large number of images to be taken by the cameras on the lander and the arm. Some of the images we already have, indicate that part of the mole is actually visible. The consensus is that the mole is about 30 cm in the regolith and probably still 7cm in the tube of the support structure. It is approximately pointing 15° away from the vertical and has undergone either some rotation or precession of its rotation axis.
It is still healthy but, of course, Its life time is limited - in terms of hammering strokes it can make before it is worn down - although we are not concerned that it would breake soon. Still, the team wants to play it safe and get all the evidence that could become available including seismic data together to see how we can help the mole to overcome the obstacle (or to get through a possible layer of gravel). Once we have all the data, we will decide on how to proceed best.
Logbook entry: 5 March 2019
The mole is healthy and performed a round of hammering on the weekend. It has, thus far, continued to work against some resistance without clear evidence for progress. The team has therefore decided to pause the hammering for about two weeks to allow the situation to be analyzed more closely and jointly come up with strategies for overcoming the obstacle.
In the meantime, we are planning on carrying out thermal conductivity measurements for the first time on Mars and start to conduct observations of the shadow of Phobos, which will be travelling through the radiometer’s field of view on 5, 6 and 8 March 2019. A lot to do and still a lot of excellent science to be expected from HP3 and from InSight! Planetary exploration is not as easy as pie!
Logbook entry: 3 March 2019
Kölle Alaaf (or Düsseldorf Helau and Meenz Helau)! Some of us on the team coming from the Rhineland centers of Carnival would now be busy partying. But commanding an instrument on Mars is even more exciting! The data that we've analyzed tell the following story about the first hammering day: It is fact that the mole is at least 18 cm out of its guiding tube and has not digged deeper than 50 cm (which would be the depth where our depth measurement device would have started recording and where the first temperature sensor on the tether would have entered the regolith.) The data show that the first 18 cm were done in about 5 minutes and they also show that the mole has been diverted away from vertical by about 15° during that time. The angle can be a few degrees larger or smaller and awaits confirmation after deeper evaluation of the data. As the diversion occurred very rapidly we may conclude that the mole hit an obstacle already close to the surface that it either moved away or more likely passed but that left its attitude somewhat inclined. The mole axis additionally precessed from pointing slightly towards the left forward foot to pointing towards the right forward foot and back again. You might conclude, it worked against that obstacle. After about 5 minutes it kept its attitude mostly and continued hammering for the remainder of the hammering time. One interpretation is that it had hit another obstacle after the first 5 minutes of penetration but it may also have worked through or into a layer of pebbles or gravel. After about 3.5 hours of hammering, it precessed again and changed attitude slightly during about 10 minutes. While it worked on the first obstacle it perhaps lifted the support structure up somewhat but certainly shifted it back towards the lander by about 2 cm as was seen in the animated gif of yesterday.
So, can we better say where the mole is? Team members (Sue, Doris, Troy) used the observed tilt of the mole and the shift of the support structure to estimate its depth and found a value between 28 and 32 cm. This is consistent with the evolution of the motor temperature after sunset that cooled significantly less rapidly than the atmosphere and suggests that the mole is at least partly buried (it is 40 cm long).
What is the feeling in the team? We are a bit worried as we hit one or two obstacles so soon already but tend to be optimistic. That the mole made the first 20 cm in 5 minutes suggests a high penetration rate when unobstructed. Would it have reached even 30 cm in that time, then the penetration rate would have been perhaps unrealistically high. More realistic may be to assume that the mole made the first 20 cm or so rapidly and then penetrated slowly for about 10 cm into some gravel or that it moved an obstacle aside while penetrating 10 cm. Tests with pebbles in sand suggest that the mole takes some hours but can work itself through a layer of pebbles or move a stone out of the way. Geological evidence suggest that the regolith should be mostly sandy. So hopefully we can get past the obstacle on Sunday and get to 70 cm more easily. But we should not forget, we are moving into the unknown.
Keep your fingers crossed!
Logbook entry: 1st March 2019
The mole has hammered for its maximum 4 hours yesterday and has reached a depth of at least 18 cm and not more than 50 cm, but not the planned 70 cm. The data indicate that the mole has reached that depth within about 5 minutes but then soon encountered an obstacle (the exact depth of which is not known).
It worked against this obstacle for the remainder of the time and may have pushed it aside after 3.5 hours as indicated by a slight rotation of the mole. The thermal sensors on the mole and on the science tether indicate that the burial was not more than 50 cm (because the bottommost temperature sensor measured a temperature as expected for the air temperature).
Moreover the temperature sensors on the mole cooled at a rate that suggest that it is at least not completely in the soil. The incident with the obstacle caused the mole to incline by about 15° (to be confirmed) with respect to vertical which caused the support structure on the surface to shift by about 2 cm:
The team is busy planning another round of hammering - again a time by up to 4 hours - to be uploaded today and starting on Saturday. The results are expected to be down Sunday.
Logbook entry: 27th February 2019
The HP3Team has successfully rescheduled the first hammering and thermal conductivity measurement cycle yesterday. This will be reviewed by the JPL/CNES/DLR operations team today (Feb 27th) and then uplinked to the lander on Mars by direct X-Band link tomorrow. The mole should start hammering at shortly after 10 in the morning local Mars time which would be around 8pm in Pasadena or 5am MEZ. The data will come down Friday morning 6:30 PST or 15:30 MEZ. We will, of course, all be gathered at JPL despite our ongoing Science Team Meeting at the Huntington Library here in Pasadena. After hammering for up to 4 hours, the mole will be allowed to cool for almost 3 days to remove heat that was generated in the mole by friction during hammering.
Starting on Sunday and running into Monday the mole will do the first thermal conductivity measurement of the sand that is around it, hopefully at 70cm depth. To do so, the outer hull of the mole will be heated at constant power for 24h and the temperature rise there will be measured as a function of time. Using data from calibration in Berlin, the thermal conductivity can be determined from the time rate of change of the temperature. This will be an important measurement and will be repeated at intervals of 50cm depth thereafter as we go down. We will then have a thermal conductivity-depth profile of the soil (which is correctly called the regolith). Later, when we measure the thermal gradient, we will multiply the thermal conductivity with the thermal gradient to obtain the heat flow, the main goal of the instrument. The data should be down early Tuesday morning Pasadena time.
In addition to the first thermal conductivity measurement on Mars (as far as I know) on Sunday there will be a Phobos eclipse shadow passing through the field of view of our radiometer on early Tueday morning. This will give us a chance to measure the thermal effect of a Phobos eclipse on the surface temperature with our radiometer. There will be two more eclipses on Wednesday and Friday. You may consider consulting e.g., the Wikipedia to find out about eclipses on Mars. I include an older HRSC photo of the Phobos shadow on Mars. The eclipse will pass through comparatively quickly in 20-30 seconds.
Exciting times, stay tuned!
For more details on the experiment take a look here. This is an open access paper describing the HP3 instrument and our DLR web sites.
Logbook entry: 26th February 2019
Unfortunately, I have bad news. Yesterday, the combined InSight OPS team (it consists of JPL, DLR and CNES folks) successfully went through the command list for the day including a review of the HP3 status, the GO for hammering and the hammering commands. The particularities of Mars and Earth rotations, communications orbiter passes with up- and downlink opportunities and working hours here resulted in the commands to be planned for UHF uplink with the morning pass by the NASA Odyssey spacecraft around 6am local time which would have been about midnight in central Europe. Unfortunately, the uplink opportunity was missed yesterday evening for yet unknown technical reasons. The OPS team now plans to use an uplink opportunity by X-band directly to the lander on Thursday which results in a necessity to replan the hammering cycles by the HP3 team. Another two days of delay...
Logbook entry: 24th February 2019
I received confirmation this morning from our System Engineer Jörg Knollenberg that the mole release was successful! That is the mole is now free of its fixation that was protecting it until now from any unwanted movements. It is now ready to go! Tomorrow, Monday the 25th of February, there will be a formal review by the operations team and then the command for the mole to start hammering will be included into the list of commands that will be sent to the lander tomorrow afternoon. Hammering operations will then commence on 10 am Local Mars Time which will be Tuesday shortly before 7 pm pacific or shortly before 2 am in Germany. A confirmation of the successful hammering is expected to be uplinked with the late afternoon pass of the TGO (Trace Gas Orbiter from ESA) which will be at 8:45 am PST or 17:45 MEZ.
Logbook entry: 22nd February 2019
Update: The final GO for Mole release has just been given!
The two recent images from the InSight Fish-eye camera on the lander (ICC) and the camera on the robotic arm (IDC) show HP3 and SEIS on the surface and the arm inspecting the HP3 instrument. The arm camera has taken many more images that will be studied by JPL and DLR scientists in a few hours for a final GO for Mole Release
Logbook entry: 21st February 2019
Excitement is mounting as we are very close to the start of hammering! Yesterday, we received the images that confirm HP3 release and the entire team (all hands out!) celebrated the end of the deployment phase of the mission with a cake. Today, the camera on the arm, the IDC, will inspect the placement of HP3 and the engineering tether, the cable running to the lander. We expect to have these images by tomorrow and will assess them very carefully. Then, the firing of the frangibolts that fix the mole to the housing will be commanded and executed on Mars the following day: Mole release! On Monday, assuming that Mole release is successful – something we should learn Sunday - we will be commanding hammering. The parameters will be set such that hammering will commence at 10:00 LMST (local Mars time) on Tuesday and last for up to 4 hours. We will transmit the hammering data to Earth using a pass of the ESA Trace Gas Orbiter TGO (thank you ESA!) and receive them by 8:45 PST on Wednesday! This will be the moment we all look forward to, the Mole's first 70 centimetres into the Martian surface! Although we have tested the Mole extensively and diligently, there is still an uncertainty. This has never been done before on Mars or on another terrestrial planets. Sure, the Apollo astronauts have drilled to a depth of about 3 metres on the Moon. But theirs was not a robotic mission.
The original logbook from the Principal Investigator including older entries can be found here.
5 May 2018 saw the launch of NASA's InSight mission, in which a lander will carry out geophysical measurements directly on the surface of Mars to explore the planet's inner structure and thermal balance. DLR has contributed to this mission in the form of the Heat Flow and Physical Properties Package (HP3) instrument. On 26 November 2018, InSight touched down north of the equator, on the Elysium Planitia plain.
For the first time since the astronaut mission Apollo 17 in 1972, heat flow measurements will be carried out on another celestial body using a drilling mechanism. The main aim of the experiment is to be able to determine the thermal state of the interior of Mars using heat flow measurements taken beneath the surface. Models of Mars’ formation, chemical composition and inner structure can be checked and refined on the basis of this data. The measurements from Mars can also be used to draw conclusions about Earth’s early development.
The depth achieved by the HP3 Mole can be tracked in the virtual control room!
Follow us on Twitter to get the newest information and pictures of our #MarsMaulwurf.